THE MONSTER OF MONTEREY: Although it is believed to have gone extinct over 60 million years ago, some believe the plesiosaur -- a massive prehistoric marine reptile -- still lives today, lurking far beneath the surface of the world's deepest oceans. In 1925, the rotting carcass of the so-called Monster of Monterey -- believed by many to be a plesiosaur -- washed up on the shores of Moore's Beach in Monterey Bay, California. Its neck is said to have been almost 20 feet long. While some biologists maintain that the remains were those of a basking shark, the evidence was inconclusive. Similar remains were snared by a Japanese fishing boat in 1977 in the waters off the coast of New Zealand. However, the crew dumped the foul smelling carcass overboard before scientific tests could be conducted.

PREHISTORIC PLESIOSAURS: Today, skeletons of the carnivorous prehistoric plesiosaur found off the coast of England and Norway are on display in many natural history museums around the world. The massive reptile is estimated to have weighed as much as 25 tons and propelled itself through the water with four muscular flippers and a long tail. Its long, slender neck is similar to reported descriptions of the Loch Ness Monster. From its pointed beak to the tip of its tail, plesiosaurs are believed to have measured at least 15 feet.

DO WE REALLY KNOW? While marine biologists have made tremendous strides toward revealing the secrets of the deep, unknown worlds remain locked away from human eyes at the bottom of the earth's deepest oceans. Indeed, new species are being discovered daily. Who is to say what does or does not exist in those black depths?